1. Field of the Invention
The present invention relates generally to the operation of an access arrangement, such as a wheelchair lift, an access ramp, a moveable access arrangement, or the like, and in particular to a hydraulic system for causing the access arrangement to move between various predefined positions, such as the ground position, the deployed position, and the stowed position.
2. Description of the Related Art
In order to provide access by individuals having restricted mobility to various areas and in specific environments, an access arrangement must be used. For example, a person utilizing a wheelchair or that has diminished physical capacity may use a ramp, an elevator, an escalator, or the like. Similarly, in order to provide such a person with full access between remote locations, the mode of transportation must also be equipped with an access arrangement, such as a lift apparatus that includes a platform. This lift arrangement can be equipped on a van or similar vehicle, and is operable between a stowed position (where the platform is positioned in the vehicle), a deployed position (where the platform is extending from the vehicle at the vehicle floor level), and a ground position (where the platform is resting or adjacent the outside ground surface).
Known lift and access arrangements are available and either manufactured integrally with the vehicle, or retrofitted to an appropriate access vehicle. Depending upon the size and configuration of the access arrangement, various driving forces and lifting systems can be used, such as mechanical systems, electrical systems, hydraulic systems, electro-pneumatic systems, or combinations thereof. One of the most common lifting systems used includes hydraulic cylinders to move the platform between the stowed, deployed, and ground positions. For example, a left hydraulic cylinder and a right hydraulic cylinder may work in unison to move the platform between positions, and these hydraulic cylinders are operable through the regulated flow of hydraulic fluid thereto.
In order to provide such regulated flow of hydraulic fluid and control the operation of the hydraulic cylinders, a hydraulic circuit is provided that includes the necessary pumps and valves to control the flow of the fluid throughout the circuit. In particular, by controlling and appropriately routing the flow of hydraulic fluid throughout the circuit, and thus, controlling the flow of hydraulic fluid to and from the hydraulic cylinders, an operator is provided with the ability to cause the platform to move between appropriate positions.
For access from the vehicle to the outside environment, and in operation, the platform is urged to the deployed position, and the user moves onto the platform, whereupon the operator causes the platform to move to the ground level, such that the user can move off the platform. For reentry to the vehicle, the platform starts at the ground position, and once the user moves onto the platform, the operator causes the platform to move to the deployed position, whereupon the user moves in to the inner area of the vehicle. Once the user enters the vehicle, the operator causes the platform to be stowed, i.e., moved between the deployed position and the stowed position.
In certain circumstances, potentially unsafe situations can arise. For example, if the user is wholly on the platform, or still in the process of moving from the platform (in the deployed position) to the inner area of the vehicle, the operator may request that the platform be stowed, e.g., through the actuation of a button, switch, or the like. Obviously, if the platform begins to stow with a user wholly or partially thereon, an unsafe and dangerous situation occurs.
Therefore, there is a need to ensure that the motive or driving system, such as a hydraulic system, cannot effectively urge the platform from the deployed position to the stowed position if a person is present thereon. Certain multi-valve arrangements have been introduced that require positive activation and introduce a bypass circuit within the overall hydraulic circuit, such as the circuit shown and described in U.S. Pat. No. 7,530,226. However, such known arrangements have particular, potential failure points and inefficiencies that leave room for improvement in this area. Ensuring the safety of the users of such access arrangements is paramount, and improvements that lead to additional safety features are beneficial.